An LCD device needs a backlight module and an LCD panel, and the backlight module needs some optical films which play the role of atomization, brightening, etc. Because the backlight module is vertically used in general, the aforementioned optical films are required to be positioned. For example, the China patent for invention whose patent number is 200410091576.X and whose title is combining structure of optical films and rubber frame mentions various positioning structures. In the prior art, the optical films are positioned on the rubber frame; because the optical films are thin in general and about 0.1-0.6 mm, in the backlight modules of small and medium size, the optical films are positioned by leaning. However, in the backlight modules of large size, because the size of the optical films is large, self weight deformation is produced among the optical films, the optical films cannot be positioned by leaning. In the prior art, the problem of self weight deformation of the optical films is solved by hanging position. Convex lugs of the optical films are drilled with holes, the optical films are directly hung on the rubber frame, but the size of the edges of the holes cannot be too small, otherwise there are difficulties in the process. The patent for invention further discloses a scheme of a convex lug arranged on one optical film, and the convex lug includes a root and an expanded part. The optical film is hung on a protrusion of the side wall of the rubber frame via the convex lug. The structure is suitable for a backlight module with a narrow frame. However, the above two positioning modes did not solve the positioning problem of the optical films in the direction perpendicular to the plane of the optical films, thereby possibly causing the warpage of the optical films. Under normal conditions, because of small deformation of the optical films in the backlight modules of small size, adhesive tapes can be employed to adhere the optical films to the rubber frame. However the adhering mode of adhesive tapes does not fit for the backlight modules of large size because the optical films have limited adhering positions, the adhering force of the adhesive tapes is inadequate, so that a certain hidden danger will exist. In the backlight modules of large size, elastic metal sheets are generally employed to clamp the optical films onto the rubber frame. However, the elastic metal sheets do not have the cost advantage because of high cost.